>>282162131
>a self sufficient city ship that somehow lasts the untold eons
Hell, even this wouldn't work. Imagine if, today, a colony ship with light speed capabilities was launched for a target 50 light years away. The crew that was alive by the time the ship made it would have lived their whole lives on the ship. Sure, there may be some 70 and 80 year olds who were in charge when the ship launched, but they'd be out of power by the time they arrived. Can we really expect the new people to stick to the plan derived by humans on a planet they've never been too? And that's just 50 light years away, imagine more.
Personally, I think humans are never leaving the Solar System. That's fine, there's a ton of resources in here (I always love the idea of Jupiter mining), but I don't think setting up civilization outside of our Sun is realistic.